Heretofore, as a typical photosensitive substance to be incorporated in photosensitive coating layers of photosensitive lithographic printing plates and photosensitive screen printing plates, a condensate (so-called diazo resin) of diphenylamine-4-diazonium salt (or 4-phenylamino-benzene-diazonium salt) and formaldehyde have been used. Production methods for such a polyfunctional diazo condensate are described in specifications of U.S. Pat. Nos. 2,679,498; 2,922,715; 2,946,683; 3,050,502; 3,311,605; 3,163,633; 3,406,159; and 3,277,074. These diazo condensates, although having many advantageous properties as practical photosensitive substances, have problems which have yet to be solved.
A first problem is that these diazo condensates are poorly soluble in organic solvents. This is especially true when inorganic ions such as halides, sulfates, or phosphates are used as counterions to the diazonium group of these diazo compounds and, when sulfonate ions such as benzenesulfonic acid, toluenesulfonic acid, or an alkylsulfonic acid are used, their solubility is insufficient in such organic solvents as glycol ethers, alcohols, ketones and the like. Such low solubility in organic solvents is a problem with these diazo condensates when used as photosensitive agents in photosensitive lithographic printing plates.
Various investigators have attempted to solve this problem. For example, Japanese Patent Publication 53-24449/1978 discloses the use of a special compound such as 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid as a counterion to the diazonium group, which enhances the solubility in organic solvents.
Japanese Patent Publication 49-45323/1974 discloses the use of a special compound such as 4,4'-bismethoxymethyl-diphenylether as a condensation agent for diphenylamine-4-diazonium salt in place of formaldehyde, which provides the same improvement. Furthermore, Japanese Patent Publication Laid-open 2-3049/1990 discloses the use of hexamethoxymethyl-melamine as a special condensation agent.
A second problem is that, since diazo condensate using diphenylamine-4-diazonium salt as a basic structural unit absorbs visible light in the region of 420-500 nm, it tends to decompose as a result. Thus, it is difficult to handle it under visible light even free from ultraviolet; this constitutes a disadvantage for production and use.
As a method which simultaneously solves the second and first problems, a novel polyfunctional diazo compound has been considered which basically differs in chemical structure from that of prior art diazo compounds. The thus obtained novel diazo compound comprises 4-dialkylaminobenzene-diazonium salt as a basic structural unit, in place of the conventional diphenylamine-4-diazonium salt.
For example, Japanese OPI (Patent Publication Laid-Open) 54-30121/1979 and Japanese OPI 61-273538/1986 use two or more 4-dialkylaminobenzene-diazonium salts, which are ester bonded to form a photosensitive polyfunctional diazonium salt. Further, Japanese OPI 1-57332/1989 uses 4-dialkylaminobenzene-diazonium salt, which is bonded in the form of a polyalkylamine to form a photosensitive polyfunctional diazonium salt. However, although these novel types of photosensitive polyfunctional diazo compounds have advantageous properties, their production is generally not easy. Furthermore, diazo compounds which are made polyfunctional by ester bonding in the above two OPI's have a problem in that the ester bond tends to be hydrolyzed.
A third problem is that diazo compounds used for photosensitive screen printing plates are essentially required to have a high solubility in water. In this respect, no diazo compounds have been reported which perform better than the prior art diazo compounds comprising a diphenylamine-4-diazonium salt condensed with formaldehyde. In Japanese OPI 2-11198/1990, diphenylamine-4-diazonium salt is condensed with formaldehyde to obtain highly water-soluble polyfunctional diazo compounds. However, these compounds have been developed to improve the developability of the lithographic printing plate after exposure with an alkaline aqueous solution, but do not provide an improvement for screen printing.
A fourth problem is that currently used condensates of diphenylamine-4-diazonium salt with formaldehyde are insufficient in photosensitivity, and a fifth problem is that the above condensates are low in transparency after exposure, or tend to be colored by heating after exposure. Such coloration has been a major problem in applications which require high transparency such as color proof and color filters, and its improvement has been in demand.
As described above, the prior art compounds have problems which have yet to be solved. Including a primary object of the present invention, these problems are summarized as follows:
1) Development of a photosensitive polyfunctional diazo compound which can be handled under visible light free from ultraviolet. PA1 2) Development of a photosensitive polyfunctional diazo compound which, as a photosensitive agent for a lithographic printing plate, is high in solubility in appropriate organic solvents, and is easy to be developed with a developing solution mainly comprising an alkaline aqueous solution. PA1 3) Development of a photosensitive polyfunctional diazo compound which is highly water soluble and suitable as a photosensitive agent for screen printing plate. PA1 4) Development of a photosensitive polyfunctional diazo compound which is high in photosensitivity. PA1 5) Development of a photosensitive polyfunctional diazo compound which is high in transparency after exposure and after exposure and heating. PA1 6) Development of a photosensitive composition which effectively utilizes the properties of the thus obtained novel polyfunctional diazo compound(s). PA1 a) Improvement of water resistance and resolution of a coating film for a screen or color proof for screen printing obtained by using the diazo compound as a photosensitive substance. PA1 b) When the diazo compound is used as a photosensitive substance for a lithographic printing plate, improvement of solubility of the diazo compound in solvents and of storage stability of the coating film on the resulting printing plate. PA1 R.sup.1 and R.sup.2 are independently hydrogen, or alkyl or alkyloxy having 1 to 8 carbon atoms; PA1 G.sup.1 is a substituent derived from alcoholic hydroxyl group; PA1 G.sup.2 is hydroxyl or the same group as G.sup.1 ; PA1 Q is a polyvalent group generated by reacting a compound having a reactivity to at least two oxiranes with carbon of the oxirane ring; PA1 Q.sup.1 is a monovalent group generated by reacting a compound having a reactivity to oxirane with carbon of the oxirane ring; PA1 R.sup.3 is alkyl or substituted alkyl having 1 to 8 carbon atoms, aralkyl or substituted aralkyl having 7 to 14 carbon atoms, or Q.sub.1 --CH.sub.2 CHG.sup.2 --CH.sub.2 --; PA1 X.sup.- is an anion based on protonic acid from which a proton is removed. ##STR4## wherein n.sup.1 to n.sup.i are integers from 0 to 10; n.sup.1 +n.sup.2 +n.sup.3 + . . . +n.sup.i =2 to 20; R.sup.1, R.sup.2, R.sup.3 and X.sup.- are respectively the same as those in Formula (I); PA1 G.sup.2 is hydroxyl or the same group as G.sup.1 in Formula (I), and the number of hydroxyl groups represented by G.sup.2 in one molecule of a diazo compound of Formula (II) is 0 to 10, and the number of groups which are the same as G.sup.1 is 2 to 20; PA1 Q.sub.2.sup.1 to Q.sub.2.sup.i and Q.sub.s are the same or different groups, and are divalent groups generated by reacting a compound in which one molecule is reactable with the carbons of two oxirane rings; PA1 R.sup.4 is the same as Q.sub.1 or G.sup.2 in Formula (I), or Formula (III). ##STR5## wherein X.sup.-, R.sup.1, R.sup.2, and R.sup.3 are the same as in Formula (I). PA1 1) High photosensitivity, PA1 2) High storage stability, PA1 3) Maximum absorption wavelengths due to 4-(N,N-dialkylamino)benzenediazonium, in the range from 372 to 382 nm (depending on the type of solvent), but almost no absorption in the visible light region. Therefore, they can be handled under white light. PA1 4) Nearly colorless photodecomposition products. PA1 1) By selecting a hydrophobic group such as chlorine, alkyloxy, or aralkyloxy as the substituent G.sup.1 of Formula (I), the water resistance of the printing plate (for example, screen printing plate) obtained using the polyfunctional diazo compound can be improved. The compound of Formula (1) is a practical example of this kind. PA1 2) By selecting a hydrophilic group such as carboxyalkyloxy or carboxyalkylcarbonyloxy as the substituent G.sup.1 of Formula (I), the developability with a developing solution mainly comprising water of the printing plate obtained using the polyfunctional diazo compound can be enhanced. From this point of view, the diazo compounds of Formulae (2) and (4) are suitable as diazo compounds for lithographic printing plates. PA1 (A) inorganic alkaline agents such as sodium silicate, potassium silicate, potassium hydroxide, sodium hydroxide, lithium hydroxide, sodium phosphate, ammonium phosphate, hydrogen phosphate, sodium metasilicate, sodium carbonate, and ammonia; PA1 (B) organic compounds such as mono-, di, or triethylamine, mono- or diisopropylamine, n-butylamine, mono-, di-, or triethanolamine, mono-, di-, or triisopropanolamine, and ethylenediamine.
The inventors have conducted intensive studies to solve these problems and achieved the invention described in the specification of U.S. Pat. No. 5,206,349. The photosensitive polyfunctional diazo compound described in this invention has at least one group of Formula (A) in the molecule: ##STR2## wherein X.sup.-, R.sup.1 and R.sup.2 are the same as those used in the following Formula (I), and R.sup.3 indicates a group which is the same as or similar to the same symbol in Formula (I).
With the invention described in the specification of U.S. Pat. No. 5,206,349, almost all of the above prior art problems have been solved, but it is found that improvement of the following properties would be even more desirable.
The inventors have been conducted further studies to improve above a) and b) and other properties, and have achieved the present invention.